KENNEDY SPACE CENTER, Fla. — NASA saved one of its best for nearly its last. Friday’s scheduled launch of the space shuttle Endeavour — its last flight, and the second-to-last planned for any shuttle — will be carrying an ambitious and potentially pioneering particle physics experiment. The $2-billion, 7.5-ton Alpha Magnetic Spectrometer, or AMS, is destined to nestle along the backbone of the International Space Station, there to study charged particles streaming through space. Designed to hunt for exotic stuff such as dark matter and antimatter, the AMS may also make fundamental dis...